The present disclosure relates generally to medical methods and devices. More particularly, the present disclosure relates to methods and systems for accessing the carotid arterial vasculature and establishing retrograde blood flow during performance of carotid artery stenting and other procedures.
Carotid artery disease usually consists of deposits of plaque P which narrow the junction between the common carotid artery CCA and the internal carotid artery ICA, an artery which provides blood flow to the brain (FIG. 5). These deposits increase the risk of embolic particles being generated and entering the cerebral vasculature, leading to neurologic consequences such as transient ischemic attacks TIA, ischemic stroke, or death. In addition, should such narrowings become severe, blood flow to the brain is inhibited with serious and sometimes fatal consequences.
Two principal therapies are employed for treating carotid artery disease. The first is carotid endarterectomy CEA, an open surgical procedure which relies on occluding the common, internal and external carotid arteries, opening the carotid artery at the site of the disease (usually the carotid bifurcation where the common carotid artery CCA divides into the internal carotid artery ICA and external carotid artery ECA), dissecting away and removing the plaque P, and then closing the carotid artery. The second procedure relies on stenting of the carotid arteries, referred to as carotid artery stenting CAS, typically at or across the branch from the common carotid artery CAA into the internal carotid artery ICA, or entirely in the internal carotid artery. Usually, a self-expanding stent is introduced through percutaneous puncture into the femoral artery in the groin and up the aortic arch into the target common carotid artery CCA.
In both these approaches, the patient is at risk of emboli being released into the cerebral vasculature via the internal carotid artery ICA. The clinical consequence of emboli release into the external carotid artery ECA, an artery which provides blood to facial structures, is less significant. During CEA, the risk of emboli release into the internal carotid artery ICA is minimized by debriding and vigorously flushing the arteries before closing the vessels and restoring blood flow. During the procedure while the artery is opened, all the carotid arteries are occluded so particles are unable to enter the vasculature.
In carotid stenting CAS procedures, adjunct embolic protection devices are usually used to at least partially alleviate the risk of emboli. An example of these devices are distal filters, which are deployed in the internal carotid artery distal to the region of stenting. The filter is intended to capture the embolic particles to prevent passage into the cerebral vasculature. Such filtering devices, however, carry certain limitations. They must be advanced to the target vessel and cross the stenosis prior to deployment, which exposes the cerebral vascular to embolic showers; they are not always easy to advance, deploy, and remove through a tight stenosis and/or a severely angulated vasculature; and finally, they only filter particles larger than the filter pore size, typically 100 to 120 μm. Also, these devices do not filter 100% of the flow due to incomplete wall opposition of the filter, and furthermore there is a risk of debris escape during filter retrieval.
Of particular interest to the present disclosure, an alternative method for reducing the risk of emboli release into the internal carotid artery ICA has been proposed for use during carotid stenting CAS procedures utilizing the concept of reversing the flow in the internal carotid artery ICA to prevent embolic debris entering the cerebral vasculature. Although a number of specific protocols have been described, they generally rely on placing a sheath via the femoral artery (transfemoral access) into the common carotid artery. Flow in the common carotid artery is occluded, typically by inflating a balloon on the distal tip of the sheath. Flow into the external carotid artery ECA may also be occluded, typically using a balloon catheter or balloon guidewire introduced through the sheath. The sheath is then connected to a venous location or to a low pressure external receptacle in order to establish a reverse or retrograde flow from the internal carotid artery through the sheath and away from the cerebral vasculature. After such reverse or retrograde flow is established, the stenting procedure may be performed with a greatly reduced risk of emboli entering the cerebral vasculature.
An alternate system which simply halts forward flow in the ICA consists of a carotid access sheath with two integral balloons: an ECA occlusion balloon at the distal tip, and a CCA occlusion balloon placed some fixed distance proximal to the ECA balloon. Between the two balloons is an opening for delivery of the interventional carotid stenting devices. This system does not reverse flow from the ICA to the venous system, but instead relies on blocking flow and performing aspiration to remove embolic debris prior to establishing forward flow in the ICA.
While such reverse or static flow protocols for performing stenting and other interventional procedures in the carotid vasculature hold great promise, such methods have generally required the manipulation of multiple separate access and occlusion components. Moreover, the protocols have been rather complicated, requiring many separate steps, limiting their performance to only the most skilled vascular surgeons, interventional radiologists and cardiologists. In addition, due to the size limitations of the femoral access, the access devices themselves provide a very high resistance to flow, limiting the amount of reverse flow and/or aspiration possible. Furthermore, the requirement to occlude the external carotid artery adds risk and complexity to the procedure. The balloon catheter for occluding the external carotid artery can become trapped in the arterial wall in cases where the stent is placed across the bifurcation from the common carotid artery to the internal carotid artery, and may cause damage to the deployed stent when it is removed.
None of the cerebral protection devices and methods described offer protection after the procedure. However, generation of embolic particles have been measured up to 48 hours or later, after the stent procedure. During CEA, flushing at the end of the procedure while blocking flow to the internal carotid artery ICA may help reduce post-procedure emboli generation. A similar flushing step during CAS may also reduce emboli risk. Additionally, a stent which is designed to improve entrapment of embolic particles may also reduce post-procedure emboli.
In addition, all currently available carotid stenting and cerebral protection systems are designed for access from the femoral artery. Unfortunately, the pathway from the femoral artery to the common carotid artery is relatively long, has several turns which in some patients can be quite angulated, and often contains plaque and other diseases. The portion of the procedure involving access to the common carotid artery from the femoral artery can be difficult and time consuming as well as risk generating showers of embolic debris up both the target and the opposite common carotid artery and thence to the cerebral vasculature. Some studies suggest that up to half, or more, of embolic complications during CAS procedures occur during access to the CCA. None of the protocols or systems offer protection during this portion of the procedure.
Recently, a reverse flow protocol having an alternative access route to the carotid arteries has been proposed by Criado. This alternative route consists of direct surgical access to the common carotid artery CCA, called transcervical access. Transcervical access greatly shortens the length and tortuosity of the pathway from the vascular access point to the target treatment site thereby easing the time and difficulty of the procedure. Additionally, this access route reduces the risk of emboli generation from navigation of diseased, angulated, or tortuous aortic arch or common carotid artery anatomy.
The Criado protocol is described in several publications in the medical literature cited below. As shown in FIG. 3, the Criado protocol uses a flow shunt which includes an arterial sheath 210 and a venous sheath 212. Each sheath has a side arm 214, terminating in a stopcock 216. The two sheaths stopcocks are connected by a connector tubing 218, thus completing a reverse flow shunt from the arterial sheath 210 to the venous sheath 212 The arterial sheath is placed in the common carotid artery CCA through an open surgical incision in the neck below the carotid bifurcation. Occlusion of the common carotid artery CCA is accomplished using a temporary vessel ligation, for example using a Rummel tourniquet and umbilical tape or vessel loop. The venous return sheath 212 is placed in the internal jugular vein UV (FIG. 3), also via an open surgical incision. Retrograde flow from the internal carotid artery ICA and the external carotid artery ECA may then be established by opening the stopcock 216. The Criado protocol is an improvement over the earlier retrograde flow protocols since it eliminates the need for femoral access. Thus, the potential complications associated with the femoral access are completely avoided. Furthermore, the lower flow restrictions presented by the shorter access route offer the opportunity for more vigorous reverse flow rate, increasing the efficiency of embolic debris removal. Because of these reduced flow restrictions, the desired retrograde flow of the internal carotid artery ICA may be established without occluding the external carotid artery ECA, as required by the earlier protocols.
While a significant improvement over the femoral access-based retrograde flow protocols, the Criado protocol and flow shunt could still benefit from improvement. In particular, the existing arterial and venous sheaths used in the procedure still have significant flow restrictions in the side arms 214 and stopcocks 216. When an interventional catheter is inserted into the arterial access sheath, the reverse flow circuit resistance is at a maximum. In some percentage of patients, the external carotid artery ECA perfusion pressure is greater than the internal carotid artery ICA perfusion pressure. In these patients, this differential pressure might drive antegrade flow into the ICA from the ECA. A reverse flow shunt with lower flow resistance could guarantee reversal of flow in both the ECA and ICA despite a pressure gradient from the ECA to the ICA.
In addition, there is no means to monitor or regulate the reverse flow rate. The ability to increase and/or modulate the flow rate would give the user the ability to set the reverse flow rate optimally to the tolerance and physiology of the patient and the stage of the procedure, and thus offer improved protection from embolic debris. Further, the system as described by Criado relies on manually turning one or more stopcocks to open and close the reverse flow shunt, for example during injection of contrast medium to facilitate placement of the CAS systems. Finally, the Criado protocol relies on open surgical occlusion of the common carotid artery, via a vessel loop or Rummel tourniquet. A system with means to occlude the common carotid artery intravascularly, for example with an occlusion element on the arterial access sheath, would allow the entire procedure to be performed using percutaneous techniques. A percutaneous approach would limit the size and associated complications of a surgical incision, as well as enable non-surgical physicians to perform the procedure.
For these reasons, it would be desirable to provide improved methods, apparatus, and systems for performing transcervical access, retrograde flow and flushing procedures and implantation of a carotid stent in the carotid arterial vasculature to reduce the risk of procedural and post-procedural emboli, to improve the level of hemostasis throughout the procedure, and to improve the ease and speed of carotid artery stenting. The methods, apparatus, and system should simplify the procedure to be performed by the physician as well as reduce the risk of improperly performing the procedures and/or achieving insufficient retrograde flow and flushing to protect against emboli release. The systems should provide individual devices and components which are readily used with each other and which protect against emboli-related complications. The methods and systems should also provide for convenient and preferably automatic closure of any and all arterial penetrations at the end of the procedure to prevent unintended blood loss. Additionally, the systems, apparatus, and methods should be suitable for performance by either open surgical or percutaneous access routes into the vasculature. Additionally, the methods, apparatus, and systems should enable implantation of an intravascular prosthetic implant which lowers post procedural complications. At least some of these objectives will be met by the inventions described herein below.